W. C. Roentgen discovered X-radiation by the exposure of a silver halide imaging element. In 1913, Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation (X-rays). Today, radiographic silver halide films account for the majority of world-wide medical diagnostic images. Such films provide viewable black-and-white images upon imagewise exposure followed by processing with the suitable wet developing and fixing photochemicals.
In medical radiography an image of a patient's anatomy is produced by exposing the patient to X-rays and recording the pattern of penetrating X-radiation using a radiographic film containing at least one radiation-sensitive silver halide emulsion layer coated on a transparent support. An approach to reducing patient exposure is to employ one or more phosphor-containing intensifying screens in combination with the radiographic film (usually both in the front and back of the film). An intensifying screen absorbs X-rays and emits longer wavelength electromagnetic radiation that the silver halide emulsions more readily absorb.
Another technique for reducing patient exposure is to coat two silver halide emulsion layers on opposite sides of the film support to form a “dual coated” radiographic film so the film can provide suitable images with even less exposure. Of course, a number of commercial products provide assemblies of both single- and dual-coated films in combination with one or two intensifying screens to allow the lowest possible patient exposure to X-rays. Typical arrangements of film and screens are described in considerable detail for example in U.S. Pat. No. 4,803,150 (Dickerson et al.), U.S. Pat. No. 5,021,327 (Bunch et al.), and U.S. Pat. No. 5,576,156 (Dickerson).
Medical radiographic X-radiation films are currently manufactured with several different contrasts in order to meet the diverse radiographic imaging needs. These include high contrast films such as commercially available Carestream Health TMAT-G Film and low contrast films such as Carestream Health TMAT-L Film. High contrast films are designed to image anatomy parts that exhibit a narrow range of X-radiation absorbance (such as bones). Medium and low contrast films are designed to image simultaneously several different types of anatomy having different X-radiation absorbance. Radiography of the thoracic cavity (chest) is an example of this need where radiologists need to image the relatively radio-opaque mediastinal area (behind the vertebral column, heart, and diaphragm). These areas are quite dense and require greater amounts of X-radiation for desired penetration and imaging on a film. However, it is also desired to image the more radio-transparent lungs. Such imaging requires less X-radiation. Carestream Health InSight™ IT Film and Carestream Health InSight™ VHC Film, and the appropriate intensifying screens, are low crossover systems designed to record this wide range of tissue densities with high imaging quality and varying exposure latitude. In these low-crossover systems, the dual-coated silver halide layers are predominantly exposed by the X-ray intensifying screen closest to the layer.
X-ray radiographic films containing blue-tinted dyes have been utilized for several decades. A primary reason for such dyes is to improve the image tone of the resulting radiographic images. Radiographic images formed by exposure to X-rays on an X-ray radiographic film consist of silver deposits that have a yellow-brown appearance that is objectionable to many radiologists. The resulting color from the developed silver can be measured using spectral absorption techniques, and is measured as a higher absorbance in the blue portion of the visible spectrum. In order to compensate for this color, blue-tinting dyes are added to the film, thereby increasing the spectral absorbance in the green and red portions of the visible spectrum. The result is a radiograph with an acceptable blue-red appearance, i.e. improved image tone.
Addition of blue-tinting dye also has the effect of increasing film Dmin or total optical density of the unexposed or low-exposure region of a processed radiographic film. The Dmin value, as measured after film exposure and processing, is generally considered to contain at least the following two factors: (1) an optical density due to the support and tinting dyes that are present before and after processing, and (2) an optical density resulting from the processing itself. For the purpose of discussing this invention, factor (2) is referred to as conventional silver fog. The Dmin value of a radiograph is considered a primary criterion for acceptable performance of a radiographic film in customer usage, as established by various standards committees that monitor performance of X-ray films in the field of medical radiography. These standard committees can be local, statewide, national, or even international organizations that set limits on various film parameters that measure the performance of X-ray films. It is generally accepted that lower Dmin value yields an improved radiograph, with higher image quality for reading details and features. Several standards committees have set acceptable limits on film Dmin to be as low as 0.25 or 0.30 for the whole lifetime of a film. These low Dmin specifications often result in reduced expiration dating of a film because the Dmin from silver fog increases with age.
U.S. Pat. No. 1,973,886 (Scanlan) describes an X-ray film including the addition of a blue tint to an X-ray base material.
U.S. Pat. No. 5,851,243 (Dickerson) patent describes the addition of a blue dye to increase neutral density in minimum density areas of an X-ray film.
U.S. Pat. No. 6,517,986 (Dickerson) describes the a* and b* values of a X-ray film containing colorants.
The publication “New Discoveries in Vision Effect Lighting Practice” by Sam M. Berman of Lawrence Berkeley National Laboratory in Berkeley, Calif. 94720 describes discoveries concerning photosensitivity of the eye.
There remains a need for improved X-ray films. In particular, there is a need for improved films for use with mammography and general-purpose radiography. Such films would have improved visual contrast, improved image quality, and/or provide the capability of improved radiographic or radiologic diagnosis.